Motors and Generators.

Magnetism and Moving charges

*Oersted had showed in the 19th century that a current carrying conductor was surrounded by a magnetic field

*Moving charges experience a force in a magnetic field

Factors that effect the magnitude of force

*F = ILBsinƒÖ

Van Allen Radiation belts - example pf motion of charged particles in a field

*Charged particles trapped inside the earth's magnetic field, which oscillate back and forth between the poles

*These charged particles experience a force due to earth's magnetic field

*Force strong perpendicular, none parallel - always has parallel and perpendicular components - there spiral out of control

Forces on Parallel wires

*Like current attract

*Unlike currents repel

*F = k I1I2

L d

The Ampere

*Defined in terms of the force between two parallel current carrying wires

*One ampere flows in each infinitely long parallel wires, separated by 1 meter in a vacuum - force exerted is 2 x 10-7

Experiment - Investigating the motor effect

*Use of a current balance - on knife edges

Motor effect

*The motion produced by the force acting in a current carrying wire in a magnetic field is called the motor effect

*'Torque experienced by a current carrying wire in a magnetic field'

Torque is defined as the turning moment of a force

*T = Fd

*Product of the force and perpendicular distance from axis to line of action of force

Forces experienced by a current carrying loop in a magnetic filed

*A current carrying loop in a magnetic field experiences a torque

*Wire is catapulted from string B to weak B

*Two long parallel wires - like currents attract, unlike repel

Radial Magnetic field

*Pole pieces of magnet are curved - thus coil always lies parallel to field - torque always max

Electric Motors

*Convert electrical energy into mechanical energy...

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